How to Build A Window Greenhouse

How to build a small window greenhouse to attach to your window for year-round growing, the article includes a building diagram, instructions and specifications.

| November/December 1987

Here's a window greenhouse that you can build in an afternoon. 

How to Build A Window Greenhouse

Plant-quality daylight may be sparse inside your home, but you need only reach out for a full helping of the sun's radiance. If you have a conveniently located double-hung window (the type with a lower sash that slides upward), there's no reason why your indoor plants can't enjoy plentiful sunlight in a window greenhouse. (See the window greenhouse diagram in the image gallery).

This miniature window greenhouse is the perfect Saturday afternoon building project and—unlike the permanent commercially available designs—fits into the window opening like a portable air conditioner. Even if you're not much of a woodworker, assembly should be painless. All that's needed is a 42 inch by 46 inch section of 3/4 inch exterior plywood, a 7 foot length of 1 by 4 pine, several feet of tapered casing or drip cap molding, the assorted hardware called out in the illustration and a 46 inch acrylic window-well cover (the kind that's used to shield basement windows). As for tools, plan on using a drill, a screwdriver and a jigsaw (to cut the wood to shape).

Begin by opening the lower window sash completely and measuring the vertical distance from the sill to the sash's lower seal, then the horizontal distance between the side casings. If a storm window is installed, be sure to allow for its frame if necessary. Use our illustration as a cutting guide, but remember that your window's dimensions are the ones that count.

The idea is to make the mounting frame slightly smaller than the window opening; a tapered drip cap and foam weather stripping will complete the seal later. The lower platform has a 3-1/2 inch extension at the rear to which the frame is attached. The framing is also fastened from the front to the face board that helps support the acrylic dome.

Once the wooden parts are cut and assembled, you can secure the dome at its lower edge with wood screws. The upper seal is caulked with silicone compound, then the lower lip is covered with a length of 1/2 inch clear plastic tubing split lengthwise and sealed at its upper edge. Use primer and an exterior latex to paint the framing and the exposed portions of the plywood. Inside, paint to match the window trim or cover the face board with a snap-in quilted fabric to match the interior. The best way to attach the greenhouse to the window frame is with four sheet metal clip plates screwed to the edge of the side framing. These can be left flat or bent inward, if necessary, to catch part of the window track.

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